System for preventing electrostatic spark discharge from a person operating an electrical appliance

ABSTRACT

In accordance with the present invention, there is provided on the handle of a vacuum cleaner nozzle, or other electrical appliance, a member of conducting material so located as to be apt to be contacted at all times during use by the hand of the operator. This member is connected to both conductors of the 120 volt circuit of the appliance through a high loss dielectric material having resistivity high enough to prevent any significant current flow at 120 volts, either between the conductors or from either conductor to the person; but low enough to permit current flow at the high voltages of a static charge from the person to the conductors and at a rate sufficiently high to drain off the charge before the voltage reaches a high enough value to produce a spark discharge, but not at a rate sufficiently high to drain off an already accumulated high static charge rapidly enough to produce a spark discharge.

[ SYSTEM FOR PREVENTKNG ELECTROSTATIC SRARK DISCHARGE FROM A PERSON OPERATTNG AN ELECTRICAL APPLIANCE [75] Inventor: Carl W. Pinkham, Jr., Stamford,

Conn.

[73] Assignee: Consolidated Foods Old Greenwich, Conn.

221 Filed: Feb.22, 1971 21 Appl.No.: 117,281

Corporation,

[52] U.S. Cl ..3l7/2 R, 317/2 B, 174/5 86 [51] Int. Cl ..H05f 3/00 [581 Field of Search....174/5 R, 5 SB, 5 SG; 317/2 R,

[56] I References Cited UNITED STATES PATENTS 7/1963 Crane ..317/2 B 12/1968 Hoover et a1. ..317/2 R Jan. 16,1973

Primary Examiner-L. T. Hix Attorney-William S. Henry [57] ABSTRACT ln accordance with the present invention, there is provided on the handle of a vacuum cleaner nozzle, or other electrical appliance, a member of conducting material so located as to be apt to be contacted at all times during use by the hand of the operator. This member is connected to both conductors of the 120 volt circuit of the appliance through a high loss dielectric material having resistivity high enough to prevent any significant current flow at 120 volts, either between the conductors or from either conductor to the person; but low enough to permit current flow at the high voltages of a static charge from the person to the conductors and at a rate sufficiently high to drain off the charge before the voltage reaches a high enough value to produce a spark discharge, but not at a rate sufficiently high to drain off an already accumulated high static charge rapidly enough to produce a spark discharge.

5 Claims, 7 Drawing Figures PATENTEDJAH 16 I975 SHEET 1 OF 2 INVENTOK CARL W. PINKHAM ATTORNEY PATENTEDJAH 16 I973 SHEET 2 BF 2 INVENTOR. CARL w. PINKHAM ATTORNEY SYSTEM FOR PREVENTING ELECTROSTATIC SPARK DISCHARGE FROM A IPERSON OPERATING AN ELECTRICAL APPLIANCE BACKGROUND OF THE INVENTION The problem of spark discharge of static electricity from the body ofa person on which it has accumulated to a grounded object or to a body of sufficient capacity to act as a static charge receiver is one of long standing. In some situations, such as in a plant manufacturing explosives, it is extremely dangerous as it may cause a most destructive explosion, but in the home it is usually merely annoying. While the voltage of the static charge may be extremely high, in the neighborhood of 5,000 volts or more, the current present in very low, and consequently the spark discharge cannot possibly cause physical injury, not even a slight burn. Nevertheless, the spark, which usually is unexpected, can be very annoying, and might cause the person to jump and possibly damage any nearby fragile object or even injure himself.

The generation of a static charge is usually caused by friction and in a home the friction frequently results from a person walking on a rug or carpet. During periods of high atmospheric humidity, such as during the summer months, the moisture present makes the rug or carpet sufficiently conductive so that the static charge drains off toground as fast as it is generated and hence does not build up in the person. However, under conditions of low humidity, as often prevail in a heated house in the Winter time, a high voltage static charge does accumulate and is suddenly discharged by a spark when the person happens to approach contact with a grounded object such as a radiator or a switch, or other static charge receiver.

Another common cause of the generation of static electricity is the operation of cleaning a rug or carpet by a vacuum cleaner as this involves not only walking back and forth, but also repeated strokes of a suction nozzle over the rug or carpet. A very popular type of vacuum cleaner has a dust bag and a motor driven fan in a unit which sets on the floor and is connected to the suction nozzle by a flexible suction hose. Moreover, many of these vacuum cleaners employ a motor driven brush in the nozzle and electric power for operating this latter motor is transmitted from the unit on the floor through conductors built into the hose. While these conductors are insulated heavily enough to prevent any possibility of electric shock from the 120- volt circuit in the hose to a person grasping the hose, it has been found that a spark discharge from a person carrying a static charge which may be 5,000 volts or more, may take place to the capacitances created by the high dielectric strength materials constituting the hose such as a nylon carcass and a polyethylene outer braid, or to ground by the route of arcing over air gaps and thence to the house ground via the l-volt circuit of the cleaner. While this can cause no physical injury, as previously explained, it can cause serious fright as the average person who is not technically trained, is apt to assume that the spark is the result of an insulation failure that could cause injurious shock from the 120- volt circuit in the hose.

In order to prevent such accumulation of a static charge, there are available numerous products, usually in aerosole form, for spraying on rugs and carpets.

These are hydroscopic in order to extract moisture from the air, thus making the rug or carpet slightly conductive. However, as they depend on the extraction of moisture from the air, they are least effective when the humidity is low which, as above explained, is when they are most needed. Moreover, they are not indefinitely effective, and usually have to be applied several times during a heating season.

SUMMARY OF THE INVENTION By means of the present invention, the static charge which tends to accumulate on the body of a person using a vacuum cleaner or other electrical device, is continuously drained off by contact with the member of conducting material and passes through the high loss dielectric material to the conductors of the l20-volt circuit and through one of the conductors to ground. Thus, the charge never builds up to a voltage high enough to produce a spark discharge should the person grasp the hose or approach contact with a grounded object or any metal object of sufficient capacity to act as a static charge receiver. At the same time, the operator is in no danger of receiving a shock from the l20- volt circuit inasmuch as the resistance of the high loss dielectric material is great enough to prevent the flow of any substantial current to the member of conducting material.

In addition, the time constant of the circuit through the high loss dielectric material is long enough so that if a large charge is produced and then the operator comes effectively into contact with the member of conducting material, the charge drains off without sensation of shock.

FIG. I is a perspective view of a vacuum cleaner system embodying the present invention;

FIG. 2 is a cross-sectional view on an enlarged scale taken on the line 22 of FIG. 1;

FIG. 3 is a cross-sectional view taken on the line 3 3 of FIG. 2;

FIG. 4 is a perspective view of a portion of the device shown in FIG. 3;

FIG. 5 is a cross-sectional view taken substantially on the line 55 of FIG. 2;

FIG. 6 is a view, partially in cross-section of a portion of an electrical appliance, such as an electric drill, embodying the present invention; and

FIG. 7 is a cross-sectional view ,on an enlarged scale taken on the line 77 of FIG. 6.

Referring more particularly to FIG. 1, reference character 10 designates generally the unit of a vacuum cleaner system which contains a dust bag and a suction fan driven by an electric motor. The unit is movably supported on a floor by means of wheels 12 and a skid M, the motor being supplied with electric power through a flexible electric cord 16 having a plug 18 which may be connected to any convenient outlet of the usual l20-volt house circuit. As is well known, one conductor of such a circuit is grounded, but inasmuch as the plug I8 may be inserted in the outlet in either of the two possible positions, there is no way for the ordinary user to know which conductor of the circuit in the vacuum cleaner is grounded.

Connected to the unit 10 is a flexible suction hose 20 having conductors 22 and 24 disposed spirally within the wall 26 of the hose, as is shown in FIG. 2 and 3.

These conductors are provided with the normal insulation which is sufficient to prevent the flow therethrough of any significant current at 120 volts. These conductors are supplied with power through an insulated lead or pigtail 28 which may be plugged into a receptacle on the unit It) which is connected to the l20'volt circuit in the unit.

A metal tube 30 has one end thereof inserted into the hose wall 26 and secured therein by expanded ribs 32, the other end of tube 30 extending a substantial distance beyond the end of the hose wall. Disposed around the wall 26 is a tubular collar 34 of molded plastic or other suitable insulating material. integral with the upper part of the collar 34 is a receptacle housing 36. Supported in suitably shaped grooves molded in the housing 36 are electrical contacts 38 and 40. The conductors 22 and 24 are brought out of the end of the hose wall 26, as shown in FIG. 2, 3 and 5, and are connected to shanks 46 and 48 of contact pins 42 and 44, respectively, which pins are inserted in lower rectangular recesses formed by the contacts 38 and 40, the resiliency of which provides a frictional grip on the pins. The contacts also form upper rectangular recesses which are in allignment with openings formed in the wall of a cap member 50, one of which openings is indicated by reference character 52 in H6. 2. This cap has been omitted from FIG. 3 so as to better reveal parts within housing 36.

Disposed between and in contact with shanks 46 and 48 is a block 54 of a high loss dielectric material having resistivity high enough to prevent any significant current flow at 120 volts, but low enough and of adequately long time constant to permit current flow at the high voltages of a static charge and at a rate sufficiently high to, drain off the charge before the voltage reaches a high enough value to produce a spark discharge, but not at a rate sufficiently high to drain off an already accumulated high static charge rapidly enough to result in a spark discharge.

A suitable value of the resistivity of this material is within the range of 10 to l ohms per cm. and the material may be a dielectric the resistivity of which has been decreased by the use of suitable plasticizing agents. As an example, the basic material may comprise polyvinylchloride of medium molecular weight plasticized with alkylphthalate esters, alkylsebacate esters, epoxidized fatty acids esters and combinations thereof in proportions that ensure the resistivity consistant with the compatability and stability of the mixture. An example of a resin-plasticizer combination that has desired performance characteristics consists of 100 parts polyvinylchloride (PVC), and a plasticizer comprising 71 parts dioctyl phthalate, 50 parts butylbenzlphthalate and 7 parts epoxidized soybean oil by weight proportions (a total of 228 parts). This platicized resin has a resistivity of 1.67 X ohms per cm.

Molded within the block 54 is a blade 56 of metal which is integral with a semi-circular ring portion 58. A bearing sleeve 60 of plastic having a radial flange 62 is disposed around the outwardly extending portion of tube 30. Disposed around sleeve 60 is one end of a metal tube 64 having a radial flange 66. Ring portion 58 is located between flanges 62 and 66 and hence is in electrical conducting relationship with tube 64.

Cap member 50 of housing 36 has a skirt portion 68 which, when the cap is in position, is flush with the end of tubular collar 34 and is formed with an internal groove 70 which is in alignment with and forms a continuation of a similar groove formed in collar 34. A split lock ring 72 is received within these grooves and radially overlaps flange 66 so as to retain tube 64 on the end of the hose while permitting the hose to swivel relative to the tube.

Tube 64 preferably is bent, as shown in P10. 1, the opposite end being insertable into a hollow tube or wand 74 connected to a suction nozzle 76. The latter is provided with a rotary brush driven by an electric motor which is supplied with 120 volt electric power through a cord 78 extending through a channel in wand 74 and terminating in a plug 80 having prongs 82 which may be inserted through openings 52 in cap 50 so as contact the upper rectangular portions of contacts 38 and 40.

in using the vacuum cleaner, the operator grasps the bent tube 62 in order to move the nozzle 76 back and forth over the rug. if during this use a static charge is generated in the operator as previously explained, it is continuously drained off through the metal tube 64, the ring 58, which is in sliding conductive contact with the flange 66 of the tube, and through the blade 56 and the block 54 to whichever of the shanks 46 or 48 is in the grounded side of the l20-volt house circuit. Consequently, the static charge never builds up in the operator to a voltage sufficient to cause a spark discharge should he or she grasp the hose 20 or approach contact with a grounded metal object, such as a water pipe or radiator. On the other hand, the resistivity of the block 54 is sufficiently high to prevent the flow of current at 120 volts to the operator through 56, 58, 66 and tube 64, or between the shanks 40 and 48.

Should the operator already have a high static charge when she grasps the bent end tube 64, this charge will be drained off through the material 54 at a slow enough rate to prevent a spark discharge.

In FIGS. 6 and 7, the inventionis shown as applied to a portable electric drill designated generally by reference character 100. As is well known, such a device has an electric motor which is supplied with the usual l20-volt current through a cord having a pair of conductors 104 and 106 therein. This cord enters a hollow handle 108 which is grasped by the operator when the drill is in use. Operation of the motor is controlled by a trigger switch 110 located in a convenient place relative to the handle.

Within the handle and adjacent to the rear surface thereof is a block of material 112 of the same nature as the block 54 in the first embodiment. The conductors 104 and 106, without other insulation, extend through this block and the latter is secured in close contact with a metal plate or button 114 disposed on the outer surface of the handle so as to be contacted by the hand of the operator when grasping the handle.

The operation of this embodiment is similar to that previously described. Should a static charge tend to accumulate in the body of the operator, it is bled off through the plate 114 and the block 112 to one or the other of the conductors 104 or 106 at a sufiicient rate to prevent it building up to a voltage high enough to cause a spark discharge should the operator approach 1. In a device contactable by a human body, said device including a low voltage electric power circuit having a grounded conductor, and a high loss dielectric material disposed so as to be between said conductor and the human body for draining static charge from the body to the conductor to thereby maintain the voltage level of the static charge below that required to produce a spark discharge.

2. A device as defined in claim 1 wherein the power circuit has two conductors either one of which is grounded and said high loss dielectric material is disposed between both said conductor and the human body.

3. A device as defined in claim 2 wherein said device is the suction hose of an electric vacuum cleaner system and said conductors are insulated and disposed in said hose and comprise a portion of the electric circuit of said vacuum cleaner.

4. A device as defined in claim 3 wherein said hose includes a handle having a conducting portion and said high loss dielectric material is between said conducting portion and said conductors.

5. A device as defined in claim 2 wherein said device is an electrical appliance having a handle provided with a conducting portion, and said high loss dielectric material is between said conducting portion and said conductors. 

1. In a device contactable by a human body, said device including a low voltage electric power circuit having a grounded conductor, and a high loss dielectric material disposed so as to be between said conductor and the human body for draining static charge from the body to the conductor to thereby maintain the voltage level of the static charge below that required to produce a spark discharge.
 2. A device as defined in claim 1 wherein the power circuit has two conductors either one of which is grounded and said high loss dielectric material is disposed between both said conductor and the human body.
 3. A device as defined in claim 2 wherein said device is the suction hose of an electric vacuum cleaner System and said conductors are insulated and disposed in said hose and comprise a portion of the electric circuit of said vacuum cleaner.
 4. A device as defined in claim 3 wherein said hose includes a handle having a conducting portion and said high loss dielectric material is between said conducting portion and said conductors.
 5. A device as defined in claim 2 wherein said device is an electrical appliance having a handle provided with a conducting portion, and said high loss dielectric material is between said conducting portion and said conductors. 